Table 1. Summary of Studies on Supplemental Prepartum Energy Effects on Calving Difficulty, Subsequent Reproductive Performance and Calf Growth 
 
 

Researcher

Supplementationa

Summary of Effects

 

Christenson et al., 1967	HE vs LE for 140 d Prepartum	HE increased birth wt.,dystocia, milk &  estrus activity
Dunn et al. 1969	ME vs LE for 120 d prepartum	ME increased birth wt.  and dystocia
Bellows et al. 1972	HE VS LE for 82 d prepartum	HE increased birth wt but  had no effect on dystocia  or weaning wt.
Laster & Gregory, 1973	HE vs ME vs LE for 90 d prepartum	HE increased birth wt  but had no effect on  dystocia
Laster, 1974	HE vs ME vs LE for 90 d prepartum	HE increased birth wt.  but had no effect on  dystocia
Corah et al. 1975	ME vs LE for 100 d prepartum	ME increased birth wt.,  estrus activity, calf vigor  and weaning wt. but  had no effect on dystocia
Bellows and Short, 1978	HE vs LE for 90 d prepartum	HE increased birth wt.,  estrus activity, pregnancy  rate and dcreased  post partum interval but  had no effect on dystocia
Anderson, et al. 1981	HE vs LE for 90 d prepartum	HE had no effect on  birth wt., milk or  weaning wt.
Houghton et al., 1986	ME vs LE for 100 d prepartum	ME increased birth wt. & weaning wt .  but had no effect on  dystocia

^aHE = high energy (over 100% NRC or National Research Council's recommended dietary need); ME = moderate energy (approximately 100% NRC); LE = low energy (under 100% NRC) 

Research through the years has been consistent in finding that reducing protein or energy pre-partum has virtually no effect on dystocia rates, even though birth weights may be altered in some experiments. Table 1 summarizes the effect of changing energy intakes on birth weights and dystocia rates. Please note: of the nine trials listed, seven showed increased energy pre-calving DID NOT increase calving difficulty. 

Following is a similar table summarizing the studies that have been done looking specifically at varying protein intake to the prepartum beef female. 
 

Table 2. Summary of Studies on Supplemental Prepartum Protein Effects on Calving Difficulty, Subsequent Reproductive Performance and Calf Growth 
 

Researcher	Supplementationa	Summary of Effects
Wallace & Raleigh, 1967	HP vs LP for 104 - 137 d prepartum	HP increased cow wt.,  birth wt. and conception  rate but decreased  dystocia
Bond & Wiltbank, 1970	HP vs MP throughout gestation	HP had no effect on birth  wt or calf survivability
Bellows et al. 1978	HP vs LP for 82 d prepartum	HP increased cow wt.,  cow ADG, birth wt.,  dystocia, weaning wt.  and decreased  conception rate
Anthony, et al. 1982	HP vs LP for 67 d prepartum	HP had no effect on  birth wt., dystocia or postpartum interval
Bolze, et al.1985	HP vs MP vs LP for 112 d prepartum	HP had no effect on birth  wt., dystocia,  weaning wt., milk or  conception rate but  decreased the postpartum interval

^aHP = high protein (over 100% NRC); MP = moderate protein (approximately 100% NRC); LP = low protein (under 100% NRC) 

 The futility of "calving heifers thin" is further illustrated by the following graph summarizing data on nine breeds of cattle in differing amounts of body condition at calving. Within normal body condition score ranges, birth weight of the calf is not affected by body condition of the cow. Only when wide extremes, such as very thin cattle or very obese cattle, occur do we find significant movement in birth weights. 

Figure 1. Relationship of calf birth weight to cow body condition score (BCS) in mature cows of nine breeds. (1996 NRC) 
  

Although producers and some researchers in the late 1970’s thought excessive protein or energy might be responsible for some dystocia problems, more recent research has not substantiated this theory. Therefore producers should be warned not to underfeed protein to the gestating cow in an effort to reduce calving difficulty. In fact, although not expressed in these tables, several studies have shown that low protein feeding during gestation resulted in decreased calf vigor, delayed uterine involution, increased interval to estrus and decreased conception rates following calving. These problems appear to be compounded when energy is also deficient.